As used hereinafter and in the claims, phosphoroamidothioate means phosphoroamidothioate and phosphoroamidodithioate. Certain phosphoroamidothioates are known in the art as having excellent insecticidal activity against a variety of insects. A particularly important commercial insecticide within this class of compounds is the insecticide acephate (generic name) or Orthene® (trade name), which can be systemically taken up by a plant so that insects which feed and/or live on the plant are killed, in addition to those insects which directly ingest or are contacted by the insecticide. Acephate and related compounds are described in U.S. Pat. Nos. 3,716,600, 3,845,172 and 3,914,417, which disclose that in addition to their insecticidal properties, the compounds possess very low mammalian toxicity. Orthene is commercially produced as a technical grade chemical of about 97 to 99.5% purity (typically about 98%), which is often referred to as acephate technical or acephate TG (technical grade).
Acephate technical is commercially available as a powder, which has a tendency to clump or agglomerate. In the past, acephate technical has been applied to crops as a dust (for example, after exposure to moisture via rain, dew or irrigation), or in spray form as a water solution spray. Dusts are undesirable because of airborne contamination and handling difficulties, while liquid spray formulations involve solvent and packaging expenses, and container disposal requirements that detract from commercial desirability.
In recent years, suggestions have been made to provide phosphoroamidothioates in a pellet form or other type of granule. Phosphoroamidothioate-containing pellets and granules have been proposed in U.S. Pat. Nos. 5,075,058, 5,100,667, 5,464,623, 5,298,501, 5,352,674, 5,369,100, 6,013,272, 6,337,323, 6,761,897, 6,875,381, and 6,752,943; the entire contents and disclosures of each of these patents is hereby incorporated herein by reference. Pellets and other granules have the advantages of eliminating dust problems and reducing offensive odors in comparison to powder forms because of a reduced surface area to weight ratio. However, there is a need for an improved process to produce improved granules, the improved process being more productive with less cost to produce improved granules.